1. If an interface priviously been UP goes DOWN, the time when the
interface changed would always show the current time.
2. If an active interface is removed from the system, the server would
still show the old screens and the user will not get any notice.
3. The "first run" detection would not work if more than one interface
is monitored. Now the "last_online" time is used, because this is an
"per interface" value initialized to 0 at startup.
4. The TRUE/FALSE macros are used for the return values as in the other
functions.